Crypt1, an active Ac-like transposon from the chestnut blight fungus, Cryphonectria parasitica

A moderately repetitive element was identified previously in the nuclear ge nome of the chestnut blight fungus, Cryphonectria parasitica, and has been used as a probe for population studies of the fungus. We report here that t he repetitive element is a class Il transposon of the hAT family of Activat or (Ac)-like transposable elements. The element, named Crypt1, has a size o f 3563 bp, including 21-bp terminal inverted repeats. A unique 8-bp direct repeat sequence flanking Crypt1 was identified in each of three clones exam ined. A single large ORF with the potential to encode a putative transposas e of 946 amino acid residues was deduced from the sequence of Crypt1. Based on amino acid sequence alignments, Crypt1 is most closely related to other Ac-like transposons of filamentous ascomycetes. A single transcript of app roximately 3.0 kb was identified by Northern hybridization experiments from Crypt1-containing isolates, suggesting that Crypt1 is an active element. A n isolate containing a single, possibly defective, copy of Crypt1 was ident ified in C. parasitica isolates from China; no Crypt1 transcript was identi fied in this isolate. Transposition of Crypt1 was inferred from Southern an d inverse PCR analyses of C. parasitica isolates maintained in the laborato ry, but transposition appears to be a rare event.